1. Technical Field
The present disclosure relates to a range imaging apparatus and a range imaging method using a time-of-flight (TOF) system in which distance information of a subject is obtained based on the time difference arising between signal light and reflection light when the signal light is emitted toward, reaches and reflects off the subject, and the reflection light is received.
2. Description of the Related Art
In recent years, with the size reduction of equipment and the advent of products for general consumers, more attention has been directed toward apparatuses and methods for generating an image having distance-measuring information of a subject (in the following, referred to as a range image) not only for use in the traditional fields of gaming and amusement but also in the application and technological development in various fields such as medical care and advertisements.
The methods of measuring the distance of a subject for range imaging include several methods such as range imaging based on parallax of images picked up by a plurality of cameras; and a method of illuminating a subject with a known random dot pattern and generating a range image based on a distortion of the dot pattern. As one example of these methods, there is a TOF system in which infrared light or a laser beam is emitted toward a subject and the distance to the subject is calculated (measured) based on measurement time the infrared light or the laser beam has taken to reach the subject, reflect off the subject and be received.
Obviously, the control flexibility increases in keeping with the accuracy of measuring the distance to the subject. The TOF system utilizes a signal amount obtained by exposure of light reflecting off the subject. Thus, by appropriately adjusting the emission of signal light for illumination and the exposure of reflection light to be received according to the distance from an imaging point to the subject and a surface reflectivity of the subject, it is possible to prevent received light signal from being saturated and an S/N ratio from declining, so that the accuracy of distance measurement will improve and the range imaging will be performed with enhanced accuracy.
In one conventional technology, when a highly accurate synthetic range image is to be generated, a plurality of range images with different exposures are obtained and compared pixel by pixel so as to generate the synthetic range image (see Japanese Unexamined Patent Application Publication No. 2012-225807).
In the other conventional technology, the light emission amount (power consumption) is adjusted to a minimum level necessary for measuring the distance to the subject based on distribution characteristics of distance values of the obtained range image (see Japanese Unexamined Patent Application Publication No. 2011-179997).